The present invention relates to an optical information recording medium, on which at least a reflective film and a light transmission layer are laminated, in the presented order, on the information recording surface of a support substrate, for recording and/or reproducing information on the information recording surface by a laser beam irradiated through the light transmission layer. More particularly, the present invention relates to an optical information recording medium, on which a first recording layer, an intermediate layer, a second recording layer, and a light transmission layer are laminated, in the presented order, on the information recording surface of a support substrate, for recording and/or reproducing information on the information recording surface by a laser beam irradiated through the light transmission layer.
In a prior art, JP-P1996-235638A proposes the method of setting the substrate to a thickness of about 0.1 mm. This relates to the method for increasing the numerical aperture (NA) of an objective lens to realize a high-density, high-capacity optical disc, and thus ensuring the tilt margin, which reduces because of the increased numerical aperture (NA). However, in such a method, it is difficult to maintain the shape of the 0.1 mm-thick substrate itself. For that reason, in the case of the reproduction-only optical discs, a reflective film is formed on a support substrate having guide grooves or information signal sections, like the conventional substrate. In the case of the rewritable optical discs, a combination of a reflective film and a phase changing film, or a magneto optical film, or a protective film is formed on the support substrate. Moreover, an optical transmission layer of about 0.1 mm in thickness is formed on the intermediate structure. Thus, information is recorded and/or reproduced by irradiating laser beams from the optical transmission layer side.
Aluminum alloys, such as Al—Ti and Al—Cr, have been broadly used for the optical information recording media of the type such as CDs, DVDs, CD-Rs, or CD-RWs, in which laser beams are irradiated onto the reflective film from the support substrate side. In this case, coarse grains are formed on the aluminum alloy film as the reflective film grows, thus making rough surfaces thereon. Because laser beams are irradiated from the side of the optical transmission layer formed on the reflective film to record or reproduce information, the rough surfaces cause large noises. Therefore, the problem is that the noises become an obstacle to high-density recording.
In order to solve such a problem, JP-P1999-120613A discloses the method for using an A6061 alloy, in which Mg or Si is added to Al, and forming the alloy through the ion beam sputtering method. However, merely using the A6061 alloy in the conventional ion sputtering method results in an insufficient noise reduction effect or the film formation in the ion-beam sputtering method results in a complicated production apparatus, so that the medium becomes costly.
Furthermore, JP-P2000-109943A discloses that an alloy containing Ag acting as a principal component, Pd, Cu, and Cr is used. This method can provide a high noise reduction effect, but tends to generate sulfuration and has a large problem on corrosion resistance. Particularly, the phase change optical disc has the problem in that when common ZnS—SiO2 is used as a protective film, sulfuration causes corrosion.